1. Field of the Invention
This invention relates generally to telecommunications, and more particularly, to wireless communications.
2. Description of the Related Art
Mobile communication systems are increasingly being utilized to transfer information, such as data, voice, text or video, among communication devices on a wireless network. To this end, a number of standards for network technologies and communication protocols have been proposed or suggested, rendering a variety of services to users. For example, third generation partnership project (3GPP) standardization has been introduced to provide IP based multimedia services to users based on the Universal Mobile Telecommunications System (UMTS) standard in a radio access network, such as a UMTS Terrestrial Radio Access Network (UTRAN).
A wireless communications system, for instance, a spread spectrum wireless communications system, such as code division multiple access (CDMA) system may allow multiple users to transmit simultaneously within the same wideband radio channel, enabling frequency re-use based on a spread spectrum technique. When moving within a particular wireless networks, such as a digital cellular CDMA network, a handover of mobile communications occurs for user equipment (UE) upon a user leaving an area of responsibility of a first cell, and into a new cell.
In a CDMA system, load control generally relates to maintaining a desired link quality level for existing users by avoiding too many users to be admitted into a single cell. The load control limits instances of user calls being dropped, in a particular cell, and may reduce affects on neighboring cells due to an inter-cell interference. Some common load control algorithms set a threshold for usage of a system resource. Examples of such a system resource include an estimate of power for each link or total transmit power for a base station, codes, number of users, throughput, and an interference level, or a combination thereof. A load control algorithm admits a user in a cell or allows a user to initiate a call as long as an estimate of a certain system resource, such as an uplink load between a mobile station and a base station, does not exceed a threshold.
Load measurement is one aspect of UMTS radio resource management that involves call admission control, congestion control and dynamic bearer control. In a CDMA system, such as based on the UMTS standard, a CDMA load may be measured by interference or power measurements. A load control may involve an uplink load measurement, which is based on uplink interference. Within a UMTS coverage area, the uplink load measurement is also known as received signal strength indicator (RSSI), which is measured in dBm.
In a UMTS Terrestrial Radio Access Network (UTRAN) device, spikes or sudden increases or changes may occur in a measurement of a system load in a CDMA system. For example, the load measurement spikes may be generated by sources, which are not under a power control of the CDMA system. Likewise, the sudden increases or changes in the load measurement may be caused by variations of the CDMA system load, e.g., due to a handover or user activity. As specified in the UMTS 3GPP standard, the load measurement is filtered and pre-processed in a base station, e.g., a Node-B and then reported to a radio network controller (RNC) via a message referred to as a measurement reporting message.
FIG. 2 shows a typical way of handling an uplink load by using one or more load control algorithms in the RNC. As such, the two common load control algorithms include an admission control algorithm, which is applied to prevent the CDMA system from becoming overloaded, and a congestion control algorithm, which is used to bring the CDMA system back into a stable operating condition. In this approach, an uplink load measurement is first converted into a CDMA system load via noise rise. Then, depending on a particular outcome from the load control algorithms, several load control actions may be performed.
Referring to the example depicted in FIG. 2, a set of load control actions for different regions of load may be summarized as follows: (A) in a low load region, e.g., when load< a Dynamic Bearer Control threshold (thr_DBC), the admission control algorithm admits all new traffic requests; (B) in a medium load region, e.g., when a thr_DBC<=load< a Call Admission Control threshold (thr_CAC), the admission control algorithm admits only traffic requests with lower resource consumption, that is, requests with a lower data rate; (C) in a high load region, e.g., when the thr_CAC<=load, the admission control algorithm blocks all incoming call requests; and (D) in a very high load region, e.g., when a Congestion Control threshold (thr_ConC)<=load, the congestion control algorithm reduces the offered traffic by reducing the data rate of one or several users. In the extreme case, the whole connection may be released by this procedure.
To obtain the noise rise in dB, which is used for load control, the difference between the measured RSSI and an estimated background noise (also in dBm) is determined. However, one problem of interference measurements is their sensitivity to interference fluctuations, which may occur due to many different reasons including interference from a CDMA system, interference from other mobile systems, and external interference.
Specifically, the interference from a CDMA system involves a known source of fluctuations, e.g., a mobile user itself. Using the UMTS common channels, under normal conditions, a transmit power control on a dedicated channel (DCH) may maintain the mobile user's transmit power close to a desired transmit power level. However, during establishment of a dedicated connection, an open loop power control is used on either a random access channel (RACH) or for an initial power setting on the DCH. In such a situation, to obtain a relatively fast synchronization, the initial power may be set to a value, which is higher than what may be required. Therefore, for a certain period, a wireless communication device, such as a mobile station transmits with a higher power, causing undesired interference fluctuations at a receiving end, e.g., at a base station, such as a Node B in an uplink.
Adjacent channel interference from mobile communication systems at adjacent frequency bands may cause additional interference. While an adjacent CDMA system may likely cause only a general increase in background noise, time division multiple access (TDMA) systems like Global System of Mobile Communications (GSM) may be a source of substantial fluctuating interference. External interference may cause fluctuations that may not be originated from any mobile user. For example, significant broadband pulses may result due to other types of noise, such as created by an electrical self-starter of a car, power lines, heavy current switches, arc welders, fluorescent lights, and the like.
Referring to FIG. 3, an exemplary RSSI measurement trace obtained from a field measurement is shown over a time period. The RSSI measurement trace illustrates occurrence of some relatively high, short-duration spikes in a system load measurement. As shown, the height of the spikes in a system load measurement may reach as high as 10 dB. Because of the occurrence of the high spikes, a typical load control algorithm causes a typical congestion control to drop existing calls. Such dropping of calls is indeed an undesired outcome of load control given the relatively short duration of these spikes, e.g., in a range of a few 100 milliseconds (msecs). One approach to handle the above described scenario calls for setting the filtering of the RSSI measurement to a very high filtering period. This high filtering period smoothes the spike to lower values, which may not lead to triggering of a load control. Application of high filtering periods will significantly slow the reaction of UL load control during a sudden load increase/decrease. Hence, load control will not be able to react fast enough on such changes by appropriately enabling/disabling the blocking/dropping of calls.
In another approach called an event triggered reporting, a time-to-trigger value may be set to higher values, which would make the reporting of the spikes more unlikely. Similar to higher filtering periods, the increased time-to-trigger will make load control reaction too slow on the load changes. Thus, making it more unlikely, that RSSI spikes will cause CDMA loadings to be above the load control thresholds, especially the thr_ConC. The usage of higher thresholds is risky since same CDMA systems become unstable in a loading region around and above 90%, as shown in FIG. 2. In such a high load condition, the transmit power control essentially functions inadequately, which leads to a much higher risk of dropping ongoing calls due to bad radio frequency (RF) link conditions. Accordingly, the drawbacks set forth above may result in imprecise measurements of system load in a CDMA system. That is, an inaccurate estimate and control of an uplink load may lead to inefficient resource management in many UMTS standard based products including the Node B base stations and UTRAN access networks.
The present invention is directed to overcoming, or at least reducing, the effects of, one or more of the problems set forth above.